Investigation of the effects of nano-graphite on morphological structure and thermal performances of fatty acid ternary eutectics/polyacrylonitrile/nano-graphite form-stable phase change composite fibrous membranes for thermal energy storage

Abstract

A series of electrospun polyacrylonitrile/nano-graphite (PAN/NG) composite fibrous membranes containing 0, 5 wt%, 10 wt%, 30 wt% and 50 wt% of NG additive were successfully fabricated as supporting materials, and then their mechanical properties and thermal stability were characterized by mechanical testing and thermogravimetric analyses. The five kinds of fatty acid ternary eutectics (i.e., CA-LA-PA, CA-LA-SA, CA-MA-PA, CA-MA-SA and CA-PA-SA) with the melting peak temperatures of around 20–25 °C were used as phase change materials to develop the novel ternary eutectic/PAN/NG form-stable phase change composite fibrous membranes (PCCFMs) through physical adsorption method. Scanning electron microscopy, differential scanning calorimetry and thermal performance test were employed to investigate the morphological structure and thermal performances of the developed form-stable PCCFMs. The results indicated that the NG additive not only enhanced the mechanical properties of composite fibrous membranes, but also effectively improved their thermal stability when the weight percentage of the loaded NG in the membranes was controlled in the 10 wt%. The SEM images revealed that the different types of ternary eutectic could be uniformly dispersed into the three-dimensional porous network structure of electrospun PAN/NG fibrous membranes. The DSC analysis indicated that the presence of NG additive had no significant influence on the phase change temperatures and enthalpies of the ternary eutectic/PAN/NG form-stable PCCFMs. These membranes possessed high phase change enthalpies of about 120–139 kJ/kg and an applicable melting peak temperature range of around 20–25 °C. The thermal performance tests suggested that the required melting and freezing times of form-stable PCCFMs were obviously shortened due to the formation of the efficient three-dimensional thermally conductive networks comprised of the NG molecular chains.